1. Field of the Invention
The present invention relates to an ink supply control device for printing machines and a method for controlling ink supply, specifically to an adjustment of ink volume under consideration of color impurities contained in each of the color inks.
2. Description of the Prior Art
Generally, color-printed-matters are printed with four-color inks such as cyan (C), magenta (M), yellow (Y) and black (K). FIG. 11 is a brief side view illustrating the overall structure of an offset press.
Printing plates for black, for cyan, for magenta, and for yellow are respectively disposed on each of plate cylinders 45 installed in a first-printing-unit 41, a second-printing-unit 42, a third-printing-unit 43, and a fourth-printing-unit 44.
Color printing is carried out on printing papers fed from the feeder 40 and passing through each of the printing units with the four-color inks by superimposing each of the color-inks. Each of the color-inks is printed on the printing paper as a plurality of fine dots. A variety of colors can be expressed by accurately adjusting the dot area ratios of each of the color-inks.
Inking units 55 for supplying ink to the printing plates disposed on the plate cylinders 45 are provided respectively to the first-printing-unit 41, the second-printing-unit 42, the third-printing-unit 43, and the fourth-printing-unit 44. FIG. 12 is a side view illustrating the overall structure of the inking unit and vicinity thereof. Ink is stored in an ink fountain 50 consisting of an ink fountain roller 52 and a blade 51.
The ink 10 fed via a gap 51S formed between the blade 51 and the ink fountain roller 52 is supplied to the printing plate disposed on the plate cylinder 45 through an ink roller group 53 including pluralities of ink rollers therein. A volume of the ink supplied to the printing plate can be adjusted by controlling an opening degree of the gap 51S formed between the blade 51 and the ink fountain roller 52 as a result of opening and closing the blade 51.
Dots printed on the printing papers become unexpectedly larger than they should be if a larger volume of ink than the adequate volume is supplied to the plate. This is because a variation of colors can only be expressed by accurately adjusting densities of the dots (an ink volume on the printing paper). As a result, printing accuracy may be decreased if the dots are formed inaccurate in size.
Ink supply volume to each of the printing units needs to be accurately adjusted. It is, however, hard for the operator to calibrate the ink supply volume to an adequate volume through his/her visual observations. In order to solve the problems, a conventional technique is used in which ink densities (ink volume) are measured at solid patches (patches having 100% dot area ratios) each consisting of cyan (C), magenta (M), and yellow (Y) and respectively printed on a printing paper. Ink supply volume is adjusted by controlling opening degrees of the gap 51S of the ink fountain 50 determined according to the densities thus measured.
In the case of adjusting ink volume by measuring the solid patches, the following problems may occur; 1) A phenomenon called xe2x80x9cdot gainxe2x80x9d in which the size of dots printed on the printing paper is unexpectedly increased due to viscosity of ink and other factors, and 2) Another phenomenon called xe2x80x9ctrappingxe2x80x9d in which superimposition of the color ink is in poor condition because of characteristics of the inks and improper conditions of the printing machine.
By carrying out printing with dots, a slight shift in color may be observed because of xe2x80x9cdot gainxe2x80x9d and/or xe2x80x9ctrappingxe2x80x9d. There is then a high probability of decreasing printing accuracy as well as obtaining undesired colors if ink supply volume is adjusted according to color densities measured at a solid patch. This is because solid patches are patches having 100% dot area ratios, not consisting of dots.
In order to solve the problems, Japanese laid-open publication No. SHO 62-146633 discloses a technique in which ink supply volume is adjusted according to ink densities measured at a gray patch consisting of cyan (C), magenta (M), and yellow (Y) and printed on a printing paper.
With this technique, ink supply volume can be adjusted in a relatively accurate manner because densities of the color inks can be detected in consideration of xe2x80x9cdot gainxe2x80x9d and/or xe2x80x9ctrappingxe2x80x9d as a result of printing the inks of cyan (C), magenta (M), and yellow (Y) in dots so as to superimpose them on one another.
A certain amount of color component different from the original color component of color ink (color impurity) is contained in each of the color inks as illustrated in FIG. 13A. Color-ink, such as cyan (C) does not consist solely (100%) of the color component of cyan, but also contains other color components such as magenta (M), and yellow (Y).
In FIGS. 13A and 13B, Cc, Cy, and Cm respectively represent color components of cyan, yellow, and magenta contained in cyan ink. Similarly, Mm, My, and Mc respectively represent color components of magenta, yellow, and cyan contained in magenta ink in these figures. Further, Yy, Yc, and Ym respectively represent color components of yellow, cyan, and magenta contained in yellow ink.
As described earlier, a certain amount of color-impurities are contained in each of the color inks as illustrated therein. The ratios of the color-impurities vary depending on the color ink (those color-impurities are exemplarly illustrated in the same ratios in FIGS. 13A and 13B). For instance, if the color-component of cyan on a gray patch is detected, the color density of cyan in the gray patch is measured as a total sum of color density of color-impurities of Mc and Yc each contained respectively in magenta ink and yellow ink in addition to color-component of cyan Cc contained in cyan ink.
Similarly, if the color-component of magenta on the gray patch is detected, the color density of magenta in the gray patch is measured as a total sum of the color density of Ym and Cm in addition to Mm. Further, if the color-component of yellow on the gray patch is detected, the color density of yellow in the gray patch is measured as a total sum of the color density of Cy and My in addition to Yy.
As described earlier, the ink supply volume of cyan ink, magenta ink, and yellow ink can not be adjusted based solely on the color densities of the color-component of cyan, magenta, and yellow detected from the gray patch because the ratios of the color-impurities vary depending on the color of the ink.
In order to solve such a problem, Japanese patent laid-open publication No. SHO58-45527 discloses a method for measuring ink densities and a device using the same in which the following procedures are described. Color densities of solid patches printed with color-inks of cyan, magenta, and yellow being used for actual printing are measured respectively prior to the printing, and then color densities Cc, Cm, Cy, Mm, Mc, My, Yy, Ym, and Yc are stored as predetermined values.
Thereafter, color-densities of an area where color-inks of cyan, magenta, and yellow being superimposed on one another are measured. Then, the color densities of the color-component of cyan, magenta, and yellow at the area (color-densities of each color component shown in FIG. 13B) are measured. Ink supply volumes of the color inks are then respectively adjusted in accordance with values obtained by deducting an ink supply volume representing the predetermined amount of color-impurity (predetermined values) of each of the color inks from the original ink supply volume.
During printing procedures, however, ink on the plate cylinder 45 shown in FIG. 12, which is not yet dried, could undesirably be mixed with an ink different in color stored in the ink fountain 50 as a result of transferring the ink through rollers belonging to the ink roller group 53 in a reverse manner. In that case, the amounts of color-impurities vary with time during the printing procedures.
In the conventional method and the device disclosed, the amounts of the color-impurities are set prior to the printing procedures. In the case of readjusting the ink supply volume during the printing procedures, the ink supply volume is adjusted in accordance with the amount of the color-impurities initially set even when the amounts of the color-impurities at a specific later time vary from the initial values. As a consequence, it is not possible to adjust ink supply volume accurately when performing printing with high accuracy.
It is an object of the present invention to provide an ink supply control device and a method therefor capable of carrying out accurate printing processes as a result of adjusting the ink supply volume with a high accuracy.
In accordance with characteristics of the present invention, there is provided an ink supply control device for independently adjusting the supply amount of a plurality of basic-color-inks, each of the basic-color-inks including a primary-color-component and a color-impurity-component which is identical with a primary-color-component of another basic-color-ink, the control device comprising:
a target color component amount storing portion for respectively storing a total amount of each color component at a target printed zone as a target color component total amount, the target printed zone being a zone where the basic-color-inks being incorporated are printed under an optimum ratio,
an actual color component amount measuring portion for respectively detecting a total amount of each color component as an actual color component total amount as a result of measuring an actual printed zone where the basic-color-inks being incorporated are printed;
an independent color component amount measuring portion for detecting both amounts of primary-color-component and that of color-impurity- component contained in the basic-color-ink at each of independent printed zones where the basic-color-inks are independently printed by respectively measuring the independent printed zones; and
a color component amount difference calculating portion for calculating a total differential amount of color components between the target color component total amount and the actual color component total amount;
wherein the independent color component amount measuring portion detects both an amount of the primary-color-component and that of the color-impurity-component contained in the basic-color-ink at each of the independent printed zones when the actual color component amount measuring portion detects an actual color component total amount;
and wherein ink supply amounts of each of the basic-color-inks are respectively adjusted in accordance with the total differential amount of color components, the amounts of primary-color-components and that of color-impurity-components contained therein.
Further, in accordance with characteristics of the present invention, there is provided a method of independently adjusting the supply amount of a plurality of basic-color-inks, each of the basic-color-inks including a primary-color-component and a color-impurity-component which is identical with a primary-color-component of another basic-color-ink, the method comprising the steps of:
storing a total amount of each color component at a target printed zone as a target color component total amount, the target printed zone being a zone where the basic-color-inks being incorporated are printed under an optimum ratio;
detecting a total amount of each color component as an actual color component total amount as a result of measuring an actual printed zone where the basic-color-inks being incorporated are printed;
detecting both an amount of the primary-color-component and that of the color-impurity-component contained in the basic-color-ink at each of the independent printed zones where the basic-color-inks are independently printed by measuring the independent printed zones when the actual color component amount is detected;
calculating a total differential amount of color components between the target color component total amount and the actual color component total amount; and
adjusting ink supply amounts of each of the basic-color-inks in accordance with the total differential amount of color components, the amounts of primary-color-components and that of color-impurity-components being contained therein.
While the novel features of the invention are set forth in a general fashion, both as to organization and content. Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed several exemplary embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.